1. Field of the Invention
The present invention relates generally to thermal processing of substrates during semiconductor manufacturing.
2. Discussion of the Background
The increasing sophistication of semiconductor technology, and the never ending reduction in minimum line widths, is causing process engineers to demand increasing capabilities from the equipment used to manufacture semiconductor integrated circuits. These requirements are leading in particular to a need to minimize the cumulative thermal burden of integrated circuit processes. The thermal burden is the cumulative amount of heat (in degree-minutes) absorbed by a wafer during processing.
Sources of the thermal burden include diffusion furnaces, etch and deposition processes, rapid thermal processing and annealing steps, among others. Typically, the temperature of a wafer rises during a process step to a steady state temperature, remains at that steady state temperature for a predetermined amount of time, then drops back to room temperature. Each process step thus adds to the thermal burden of the overall process. Though the peak temperature of a given process step usually contributes the most to the incremental increase in the thermal burden, the need for processes requiring lower peak temperatures is causing temperature ramp steps to contribute substantially to the thermal burden in an increasing number of cases. In some cases, there is essentially no steady state temperature. One key piece of equipment used to control the temperature of a wafer during a process step is a susceptor. Each wafer is placed sequentially on a susceptor, and the temperature of the wafer is controlled through the susceptor.
Minimizing the thermal burden in general, and precise wafer temperature control in particular, presents challenges to the manufacturers of capital equipment used to make integrated circuits. Those equipment manufacturers that can best meet the needs of the end users of semiconductor capital equipment stand to increase their market share.